Inhibitory effects of puerarin on myometrium contraction during rat menstrual cycle and its underlying mechanisms

Purpose: To observe uterine contractile patterns in various phases of the menstrual cycle, and elucidate mechanisms involved in the inhibition of puerarin on rat uterine contraction.

Methods: Uterus strips of Sprague Dawley rat were suspended in tissue chambers to measure the contractile activities of the strips.

Results: Isolated myometrial strips possessed three typical forms of contractions: spontaneous rhythmic contraction, tonic contraction, and irregular contraction, respectively appearing in varied phases of the rat menstrual cycle. Puerarin not only dose-dependently inhibited spontaneous contraction but also could dose-dependently inhibit KCl or PGF_2α-induced uterus contractions. The inhibitory effects induced by puerarin in KCl-precontracted myometrial strips could be attenuated partly by β₂ adrenoceptor antagonist ICI118551 but had no obvious changes prior to treatment with glibenclamide, N^w-L-nitro-arginine, ICI 182,780, tamoxifen or indomethacin. In high K⁺ Ca²⁺-free Kreb’s solution containing 0.01 mmol/L egtazic acid (EGTA), puerarin decreased the first phase contractions induced by oxytocin, acetylcholine, or prostaglandin F_2α, but did not affect the second contractions induced by CaCl₂, and also had no marked effect on the concentration-response curve of CaCl₂.

Conclusion: The results demonstrate that uterus contraction patterns differ during varied menstrual cycle phases. Puerarin can inhibit isolated myometrium contractions, probably due to activation of β₂-adrenoceptor, and partially via reduction of Ca²⁺ release from the sarcoplasmic reticulum.